1. Technical Field
This invention relates in general to telecommunications and, more particularly, to a method and apparatus to obtain per-hop, one-way, packet loss and delay measurements in multi-class service networks.
2. Description of the Related Art
Per-hop, one-way, packet loss and delay measurements are useful in designing and maintaining a communications network. Such measurements can reveal if a piece of equipment is faulty, or not performing to specifications.
Existing solutions for delay measurements can be categorized as active measurement techniques or passive measurement techniques. Solutions based on an active measurement technique generate test packets or probes and inject them into the network. Some active measurement solutions measure a roundtrip delay and estimate a one-way delay by halving the result. Other solutions measure a one-way delay, which is more accurate. In all cases, the one-way active measurement requires a high-precision clock synchronization in order to determine the delay.
Solutions based on a passive measurement technique traditionally observe the time difference of a packet traversing between two points. These techniques, however, need to resolve a problem of clock synchronization between the two measurement engines, usually located at two different nodes. Some solutions approach the problem by employing a centralized synchonizaton or coordination system.
The major problem with the existing solutions is an ability to accommodate a large-scale deployment on a per-hop per-aggregate basis. They are either not cost effective or network resource usage effective in the case of active measurement based solutions. Meanwhile in the case of passive measurement based solutions, they either introduce excessive complexity or employ a centralized control that would restrict a scale of deployment and be a vulnerable spot.
The prior art has many shortcomings. First, the main problem with the roundtrip delay concerns with a well-known asymmetric route connecting two points in a network. Normally, the forward route takes a difference path from the backward route. This factor challenges a validity of halving a roundtrip delay in order to infer to a one-way delay.
Second, the one-way active measurement requires a clock synchronization between two measurement points that imposes a major burden on implementation and cost. It also impedes the solution from a large-scale deployment.
Third, the nature of an active measurement itself requires injecting overhead traffic into the network. Thus to measure a one-way per hop and per aggregate delay at each link in the network is a prohibitive task and very expensive. This is one of the main reasons that significantly lessen appropriateness in adopting these existing solutions.
Fourth, the major problem that prevents a passive measurement based approach from to be a viable and efficient solution is a need of clock synchronization between two nodes to obtain the delay. Various techniques have been proposed such as a centralized coordination or a GPS (Global Positioning System)-based clock synchronization system, but the usefulness is quite restricted to a small-scale deployment.
A similar problem is present with measuring packet loss. As in the case of measuring one-way delay, existing solutions can be categorized in two classes, active or network-based. Existing active measurement solutions are based on generating a test packet or probe such as ICMP Echo/Reply packets. Others are based on a one-way active measurement that requires a clock synchronization system in addition to injecting a test packet into a network. Network-based solutions use a network management system to collect information about a packet loss. For example, they employ SNMP to gather packet loss statistics from MIB (Management Information Base) that resides and is populated by the managed node or dedicated agents. Other may employ RMON (Remote Monitoring) probes or agents to collect packet loss statistics.
The major problem with the existing solutions is an ability to support a large-scale deployment on a fine-grained per-hop and per-aggregate basis. They are either not resource usage efficient or cost effective in the case of active measurement-based solutions. In the case of network management-based solutions, they lack a desired fine grained measurement support as well as are too complex for a large-scale deployment.
Specific problems with ICMP Echo/Reply packets include: (1)—an introduction of overhead traffic into a network, (2)—a requirement of ICMP support from a measurement nodes, (3) a lack of per-aggregate measurement support, and (4) an inability to measure a packet loss within a node. The major problem with a one-way active measurement are that these solutions need a synchronization or coordination between two measurement points in addition to imposing overhead traffic onto a network. These two drawbacks prevent this class of solutions from a large-scale deployment. Network-based solutions also have significant problems: (1) they rely on a node to support MIB in order to collect statistics; moreover, the current standard MIB does not provide per-aggregate statistics, (2) they offer less flexibility and controllability to configure and perform a packet loss measurement dynamically and on a on-demand basis, and (3) they do not support a measurement of packet loss within a node.
Accordingly, a need exists for an improved technique for measuring per-hop one-way delays and per-hop one-way packet loss in multi-class service networks.